Barley lipoxygenase-1 (hereinafter, “LOX-1”) is an enzyme present in malt, which oxidizes malt-derived linoleic acid to 9-hydroperoxyoctadecadienoic acid during mashing for production of malt alcoholic beverages (Kobayashi, N. et al., J. Ferment. Bioeng., 76, 371-375, 1993). 9-Hydroperoxyoctadecadienoic acid is further converted to trihydroxyoctadecenoic acid (THOD) by peroxygenase-like activity (Kuroda, H., et al., J. Biosci. Bioeng., 93, 73-77, 2002). It is known that THOD reduces beer foam stability, imparts an astringent flavor and impairs smoothness of beer flavor (Kobayashi, N., J. Am. Soc. Brew. Chem. 60: 37-41. 2002; and Kaneda, H. et al., J. Biosci. Bioeng., 92, 221-226. 2001), resulting in lower quality of malt alcoholic beverages. In addition, 9-hydroperoxyoctadecadienoic acid is converted to trans-2-nonenal which is the substance responsible for an unpleasant cardboard flavor in aged malt alcoholic beverages (Yasui, Journal of the Brewing Society of Japan, 96:94-99 (2001)).
As a strategy for inhibiting production of trans-2-nonenal in order to improve flavor stability of malt alcoholic beverages, there has been proposed a method of producing malt alcoholic beverages using malt with low LOX-1 activity (Drost, J. Am. Soc. Brew. Chem. 48:124-131 (1990)).
Douma et al. have induced mutation in barley by mutagenic (chemical) treatment to create an induced mutated line exhibiting 9% of lower LOX-1 activity compared to controls, and have attempted to produce malt alcoholic beverages using such barley (WO02/053721).
Even when such barley is used, however, the reduced trans-2-nonenal concentration of the obtained malt alcoholic beverages is insufficient and flavor stability is not adequately improved. Furthermore, absolutely no definite results have been achieved in terms of reducing THOD or improving foam stability.